To reach Chicago Basin, use the Approach Page. From your camp in Chicago Basin, hike northeast toward the end of the basin on the great trail - Photo #1. Near 11,200’, turn left toward Twin Lakes at a signed junction - Photo #2. This trail is used to reach Windom, Sunlight, and Eolus. Continue up through the forest (Photo #3) to an area where the trail is a bit difficult to follow over and around some rock slabs - Photo #4. Near 11,400’, leave the trees where you have a great view of the two streams that flow down the slope below Twin Lakes - Photo #5. Follow the trail north up the slope and cross the first stream at 11,700’ - Photo #6. Immediately after the crossing, climb steep terrain for 300’ before the trail angles right and the slope eases. Continue northeast to the second stream crossing before 12,300’ - Photo #7, Photo #8 and Photo #9. Cross the stream and turn left to climb steeply up the slope. About 200’ after the crossing, the slope rolls over and you arrive at the south end of Twin Lakes (~12,500’) - Photo #10.
Off to your left (west), much of Mt. Eolus is in view - Photo #11 is a high-angle overview of the remaining route. From the flat area before the lakes, continue a short distance north. On the west side of the stream leading from the lakes, try to spot the trail to Eolus that heads west under some cliffs - Photo #12. Turn left, drop down and cross the stream, and start west on the new trail seen in Photo #12. If you cannot locate the trail, it’s possible you dropped down below it - walk up the hill until you intersect the solid trail below the cliffs. Once on the trail, continue west across the grassy slope. Photo #13 looks back on the area. Follow the mostly-obvious trail southwest toward the end of the basin below Eolus’ East Face - Photo #14. Continue above 13,000’ as you approach the area that provides your exit from the basin. Beyond some angled slabs to your right, there is a ramp/ledge that climbs northeast out of the basin - Photo #15. The ramp is difficult to identify until you are near the entrance. Continue on the trail and over some low-angle rock slabs to reach the base of the ramp seen in Photo #16. Studying Photo #15 and Photo #16 will help you identify this area and avoid turning right too early. Above 13,400’, reach the entrance to the ramp - Photo #17.
Turn right and climb northeast on the wide, Class 2 ramp - Photo #18. Part-way up the ramp there are a couple of sections that require careful steps across some angled slabs, but the difficulty should not exceed Class 2. At the top of the ramp, continue north up through some easy terrain to reach a flat area east of the connecting ridge between Eolus and North Eolus. To your right (east), and below, is the high basin between North Eolus and Glacier Point (13,704’).
From this flat area, your next goal is to gain the Eolus-North Eolus ridge above and to the west - Photo #19. Locate a notch in the ridge just above a short, green gully. It’s best to hit the ridge at or near this notch. While there are several ways to reach the ridge, the most direct approach is to climb the small, green gully below the notch - Photo #20. Some easier terrain is off to the right, but it requires zigzagging on angled rock slabs. After some brief Class 3 climbing, reach the notch near 13,850’ - Photo #21. From here, you have an interesting view of the remaining route to the summit - Photo #22. Eolus’ Northeast Ridge and East Face are quite obvious, but first you must cross a narrow stretch of ridge called the Catwalk. Turn left and ascend a bump on the ridge to get a full view of the Catwalk. Most of the Catwalk is Class 2 but there are a few sections that require some easy Class 3 moves to overcome small dips along the way. Carefully scramble onto the Catwalk and follow the obvious route towards Eolus - Photo #23. Taken from North Eolus, Photo #24 provides a different look at the Catwalk. After crossing the Catwalk (Photo #25), reach easier terrain below the final summit pitch - Photo #26.
The remaining 250+ feet to the summit requires plenty of route-finding and Class 3 scrambling. As seen in Photo #26, the Northeast Ridge is directly above but the easiest route to the summit does not take the ridge. From the base of the ridge, turn left and traverse under some rock walls on the East Face - Photo #27. After passing below the steep rock, begin climbing up through ledges - Photo #28. There are many ways to climb this face and you may find trail segments that lead in different directions. Generally, zigzag up the center of the face without going too far to the left or right. The more you climb to the right (toward the ridge), the more difficult terrain you will encounter. Just below the summit, the climbing becomes steeper, but still Class 3. Even with dry conditions care must be taken on the narrow ledges - Photo #29 and Photo #30. Gain the summit ridge just left (south) of the summit (Photo #31) and turn right to reach the top - Photo #32 and Photo #33.